1. Field of the Invention
The present invention relates to a copyrighted digital data management method, a contents provider, a user terminal, and a data-recording medium for managing copyrights during the use, storage, copy, and transfer of copyrighted digital data such as video, sound, and computer software.
2. Description of the Related Art
As the digital data age has arrived, various systems for providing the user with copyrighted digital data, such as video, sound, and computer software, over the Internet have been developed.
For example, in the cable broadcasting transmission system and method disclosed in Japanese Patent Laid-Open Publication No. Hei 10-257466, a data provider sends preview video before the user is going to select video data to be played back so that the user can examine the content before agreeing to pay for it.
FIG. 1 is a diagram showing the configuration of a cable broadcasting transmission system and method in the prior art.
The conventional cable broadcasting transmission system and method in FIG. 1, disclosed in Japanese Patent Laid-Open Publication No. Hei 10-257466, will be outlined below.
A data transmission central station 101 comprises a transmitter/receiver 201, a control command processor 202, an accounting manager 203, a stream data generator 204, a video data storage unit 205, and an index data storage unit 206. The video data storage unit 205 and the index data storage unit 206 respectively store therein video data and index data compressed according to the MPEG (Moving Picture Experts Group) standard. The video data and index data are digital.
In response to a playback request for video data from the user, the data transmission central station 101 reads required(requested) data from the video data storage unit 205 and generates a video stream for preview via the stream data generator 204. More specifically, the stream data generator 204 references the data stored in the index data storage unit 206, reads only the I frames (Intra-frames) from the video data storage unit 205 beginning at the start of the content for use in preview to generate a preview video stream, and sends the preview video stream to the user terminal via the transmitter/receiver 201.
After that, the user views the preview video stream displayed on the terminal and, if that video data is the one the user wants to view, sends a message, indicating that the user agrees to pay for it, to the data transmission central station 101. Upon receiving this agreement message, the data transmission central station 101 reads all video data from the start and sends the full video stream to the user terminal.
In the conventional cable broadcasting transmission system and method described above, the full video stream corresponding to the preview video stream is sent from the data transmission central station 101 after the user views the preview and sends an agreement message to the data transmission central station 101. This gives the user a chance to record the full video stream onto a data recording medium attached to the terminal for later playback.
Because the full video stream is digital data and therefore the quality is not degraded by repeated copy or transfer operations, there is a possibility that the user will make an illegal copy of the video stream and transfer it to other users.
To avoid this illegal copy or transfer, copyrighted digital data, which is transferred from a contents provider (data provider) to the user's data terminal via the Internet, is encrypted with encryption key data. This method allows only the user, who agrees to pay for digital data, to decipher the copyrighted digital data.